CVE-2024-35860: bpf: support deferring bpf_link dealloc to after RCU grace period
First published: Sun May 19 2024(Updated: )
In the Linux kernel, the following vulnerability has been resolved: bpf: support deferring bpf_link dealloc to after RCU grace period BPF link for some program types is passed as a "context" which can be used by those BPF programs to look up additional information. E.g., for multi-kprobes and multi-uprobes, link is used to fetch BPF cookie values. Because of this runtime dependency, when bpf_link refcnt drops to zero there could still be active BPF programs running accessing link data. This patch adds generic support to defer bpf_link dealloc callback to after RCU GP, if requested. This is done by exposing two different deallocation callbacks, one synchronous and one deferred. If deferred one is provided, bpf_link_free() will schedule dealloc_deferred() callback to happen after RCU GP. BPF is using two flavors of RCU: "classic" non-sleepable one and RCU tasks trace one. The latter is used when sleepable BPF programs are used. bpf_link_free() accommodates that by checking underlying BPF program's sleepable flag, and goes either through normal RCU GP only for non-sleepable, or through RCU tasks trace GP *and* then normal RCU GP (taking into account rcu_trace_implies_rcu_gp() optimization), if BPF program is sleepable. We use this for multi-kprobe and multi-uprobe links, which dereference link during program run. We also preventively switch raw_tp link to use deferred dealloc callback, as upcoming changes in bpf-next tree expose raw_tp link data (specifically, cookie value) to BPF program at runtime as well.
Credit: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 416baaa9-dc9f-4396-8d5f-8c081fb06d67
| Affected Software | Affected Version | How to fix |
|---|---|---|
| debian/linux | <=6.1.106-3<=6.1.112-1 | 5.10.223-1 5.10.226-1 6.10.11-1 6.11.2-1 |
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Reference Links
- https://git.kernel.org/stable/c/1a80dbcb2dbaf6e4c216e62e30fa7d3daa8001ce
- https://git.kernel.org/stable/c/5d8d447777564b35f67000e7838e7ccb64d525c8
- https://git.kernel.org/stable/c/876941f533e7b47fc69977fc4551c02f2d18af97
- https://launchpad.net/bugs/cve/CVE-2024-35860
- https://git.kernel.org/linus/1a80dbcb2dbaf6e4c216e62e30fa7d3daa8001ce
- https://security-tracker.debian.org/tracker/CVE-2024-35860
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-35860
- https://nvd.nist.gov/vuln/detail/CVE-2024-35860
- https://ubuntu.com/security/CVE-2024-35860
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